Grammar
Grammar rules with examples
The 20 rules behind most grammar mistakes in school writing and on the CLT and SAT, each in one plain sentence. Open a rule for examples, a quick test and practice sentences.
Updated October 29, 2026
Subject-verb agreementA singular subject takes a singular verb; a plural subject takes a plural verb.
Pronoun agreementA pronoun must match the noun it stands for in number.
Pronoun case: I or me, who or whomUse I, he, she, we, they and who as subjects; use me, him, her, us, them and whom as objects.
Comma splices and run-onsTwo complete sentences can't be joined by a comma alone.
Sentence fragmentsEvery sentence needs a subject and a main verb and must express a complete thought.
ApostrophesAn apostrophe shows ownership or a missing letter; it never makes a word plural.
Its, it's, their, there and they'reWords that sound alike: possessives have no apostrophe; contractions do.
Commas around extra informationExtra information that could be removed goes between two commas, or none at all.
Semicolons and colonsA semicolon joins two complete sentences; a colon introduces something after a complete sentence.
Commas after openers and before and, but, soPut a comma after an opening phrase, and before and, but or so when they join two sentences.
Parallel structureItems in a list or a pair must have the same grammatical form.
Misplaced and dangling modifiersA describing phrase must sit right next to the word it describes.
Verb tenseKeep the verbs in the same time unless the time really changes.
Irregular verbs and "should have"Use the right form of irregular verbs, and write should have, never should of.
ComparisonsCompare like with like, and use the right comparing word.
Adjectives and adverbsAdjectives describe nouns; adverbs describe verbs, adjectives and other adverbs.
Commonly confused wordsSome word pairs look or sound alike but mean different things.
Wordiness and repetitionSay it once, in as few words as the meaning needs.
Capital lettersCapitalize names, places, days, months, holidays, titles and the first word of a sentence.
That, which and whoUse who for people, that for essential details about things, and which (with commas) for extra details.
Practice a little every day
The Daily Grammar Fix gives everyone the same sentence each day: tap the mistake, pick the fix, read why. It takes about thirty seconds and keeps a streak.
Questions people ask
What are the most common grammar mistakes?
Comma splices, subject-verb agreement with a long phrase in the middle, its and it's, pronouns that don't match their noun, and missing commas around extra information.
How can I get better at grammar fast?
Practice a few sentences every day and read why each fix works. One rule at a time sticks better than a long list read once.
Is the Daily Grammar Fix free?
Yes. It is a free part of Owl Test Prep, with no account needed.